The polyphenylene ether resins are well known in the art as comprising a family of thermoplastic materials which are suitable for various engineering purposes. These may be made by catalyzed and non-catalyzed processes described in the patent literature, such as in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, and in Stamatoff, U.S. 3,257,357 and U.S. 3,257,358, all of which are incorporated herein by reference.
It is known that the polyphenylene ether resins may be admixed with polystyrene, either unmodified or modified, to produce compositions having properties better than those of either of the two polymers individually. Such compositions are disclosed in Cizek, U.S. Pat. No. 3,383,435, which is incorporated herein by reference.
To reduce the cost, it has been proposed to add mineral fillers such as aluminum silicate, calcium carbonate, magnesium silicate, calcium silicate, silica or others, to compositions containing a polyphenylene ether resin and polystyrene. Compositions comprising a polyphenylene ether resin, a rubber modified high impact polystyrene and aluminum silicate are disclosed in U.S. Pat. No. 4,166,812.
Copending application Ser. No. 755,025, filed Dec. 28, 1976, discloses compositions comprising a polyphenylene ether resin, alone, or in combination with an impact modifier which is not a high impact rubber modified polystyrene, a mineral filler and a plasticizer.
It is proposed in application Ser. No. 209,797 filed concurrently herewith that the Gardner impact strength of filled compositions comprising a polyphenylene ether, an impact modifier such as an A-B-A.sup.1 block copolymer and a plasticizer can be surprisingly retained if a particulate clay filler having a certain particle size is employed in such compositions.
It is known that the addition of mineral fillers to polyphenylene ether resins can increase the rigidity and dimensional stability of the polymers. The toughness of the resulting composite is usually lower than that of the mineral filler-free polymer, however. It has been found that some mineral fillers increase the rigidity of the polymer and provide ductile composites having good impact resistance. Such benefits are more pronounced in falling weight-type impact tests, such as Gardner impact resistance. This type of impact resistance is much more important in actual practice than the impact resistance as measured by other means such as the Izod impact test.
It has now been discovered that as among mineral fillers in general, titanium dioxide particles having a particle size no greater than 0.6 micron, and preferably 0.2 micron or less, provides retention of Gardner impact strength when included in a composition composed of polyphenylene ether, an impact modifier and a plasticizer, which constitutes an improvement.